Thermal transistor

ABSTRACT

A thermal transistor is provided. The thermal transistor includes a metallic thermal conductor, a non-metallic thermal conductor, and a thermal resistance adjusting unit. The metallic thermal conductor and the non-metallic thermal conductor are contact with each other to form a thermal interface. The thermal resistance adjusting unit is configured to generate an bias voltage U12 between the metallic thermal conductor and the non-metallic thermal conductor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application is related to co-pending applications entitled, “THERMALTRANSISTOR”, concurrently filed (Atty. Docket No. US72190); “METHOD FORCONTROLLING THERMAL TRANSISTOR”, concurrently filed (Atty. Docket No.US72192).

FIELD

The present disclosure relates to the field of thermal rectification,and more particularly to thermal logical device.

BACKGROUND

Interfacial thermal resistance is a measure of an interface's resistanceto thermal flow. Thermal rectification can be achieved by regulating theinterfacial thermal resistance, and on this basis thermal logical devicecan be fabricated. However, in prior art the interfacial thermalresistance cannot be effectively controlled.

What is needed, therefore, is to provide a thermal transistor and amethod for controlling the interfacial thermal resistance of the thermaltransistor.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a flow diagram of one embodiment of a method for controllingthermal transistor.

FIG. 2 is a schematic view of one embodiment of a method for controllingthermal transistor.

FIG. 3 is a schematic view of one embodiment of the metallic thermalconductor and the non-metallic thermal conductor.

FIG. 4 is a schematic view of one embodiment of carbon nanotube segmentof a carbon nanotube film.

FIG. 5 is a schematic view of one embodiment of a method for controllingthermal transistor.

FIG. 6 is a diagram of one embodiment of bias voltage-amplitude ratios.

FIG. 7 is a structural schematic view of one embodiment of a thermaltransistor.

FIG. 8 is a structural schematic view of one embodiment of a thermaltransistor.

FIG. 9 is a schematic view of one embodiment of a thermal logicaldevice.

FIG. 10 is flow diagram of one embodiment of a method for making athermal transistor.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. The drawings are not necessarily to scale, andthe proportions of certain parts may be exaggerated to be betterillustrate details and features. The description is not to be consideredas limiting the scope of the embodiments described herein.

Several definitions that apply throughout this disclosure will now bepresented.

The connection can be such that the objects are permanently connected orreleasably connected. The term “outside” refers to a region that isbeyond the outermost confines of a physical object. The term “inside”indicates that at least a portion of a region is partially containedwithin a boundary formed by the object. The term “substantially” isdefined to essentially conforming to the particular dimension, shape orother word that substantially modifies, such that the component need notbe exact. For example, substantially cylindrical means that the objectresembles a cylinder, but can have one or more deviations from a truecylinder. The term “comprising” means “including, but not necessarilylimited to”; it specifically indicates open-ended inclusion ormembership in a so-described combination, group, series and the like.

FIG. 1 and FIG. 2 show an embodiment of a method for modulatinginterfacial thermal resistance at an interface between a metallicthermal conductor 10 and a non-metallic thermal conductor 20. The methodincludes, at least the following blocks:

S11, providing a metallic thermal conductor 10 and a non-metallicthermal conductor 20, the metallic thermal conductor 10 and thenon-metallic thermal conductor 20 are in direct contact with each otherto form an interface 100; and

S12, varying an electric field at the interface 100 to modulate theinterfacial thermal resistance at the interface 100.

In block S11, both the metallic thermal conductor 10 and thenon-metallic thermal conductor 20 are made of heat conductive materials.The metallic thermal conductor 10 can be copper, aluminum, iron, gold,silver, alloy, or the like. The non-metallic thermal conductor 20 can beelectrical conductive material, such as carbon nanotubes, graphene,carbon fibers, or the like.

The metallic thermal conductor 10 is closely in contact with thenon-metallic thermal conductor 20, so heat can be transferred as much aspossible between the metallic thermal conductor 10 and the non-metallicthermal conductor 20. In order to ensure good contact, the surfaces ofthe metallic thermal conductor 10 and the non-metallic thermal conductor20 need to be smooth to create a seamless contact surface.

The metallic thermal conductor 10 and the non-metallic thermal conductor20 can be disposed in a sealed space to reduce interference from outsideairflow. In one embodiment, the metallic thermal conductor 10 and thenon-metallic thermal conductor 20 are disposed in a vacuum room.

The metallic thermal conductor 10 and the non-metallic thermal conductor20 are stacked to form the interface 100. Specifically, the metallicthermal conductor 10 and the non-metallic thermal conductor 20 could becompletely or partially overlapped. FIG. 3 shows embodiment of relativepositions of the metallic thermal conductor 10 and the non-metallicthermal conductor 20.

The shape of the metallic thermal conductor 10 is not limited. Thethickness of the metallic thermal conductor 10 can be ranged from about0.1 mm to about 1 mm. The smaller is the thickness of the metallicthermal conductor 10, the easier it is to observe the change ofinterfacial thermal resistance.

In one embodiment, the metallic thermal conductor 10 is a copper sheetwith a dimension of 15 mm in length, 15 mm in width, and 0.5 mm inthickness.

The shape of the non-metallic thermal conductor 20 is not limited. Thethickness of the non-metallic thermal conductor 20 can be ranged fromabout 30 μm to about 120 μm. The smaller is the thickness of thenon-metallic thermal conductor 20, the easier it is to observe thechange of interfacial thermal resistance. The density of thenon-metallic thermal conductor 20 can range from about 0.3 g/cm³ toabout 1.4 g/cm³.

In one embodiment, the non-metallic thermal conductor 20 is made ofbuckypaper with a dimension of 15 mm in length, 15 mm in width, and 52μm in thickness. The density of the buckypaper ranges from about 1.2g/cm³ to about 1.3 g/cm³.

The buckypaper includes a plurality of carbon nanotubes. Adjacent carbonnanotubes are joined end to end by van der Waals attractive forcetherebetween along a longitudinal direction of the carbon nanotubes. Inone embodiment, a method for making the buckypaper includes, at leastthe following blocks:

S101, providing at least one carbon nanotube array;

S102, forming a plurality of carbon nanotube films by drawing aplurality of carbon nanotubes from the at least one carbon nanotubearray; and

S103, stacking and pressing the carbon nanotube films.

In block S101, the carbon nanotube array is a super-aligned carbonnanotube array. In one embodiment, the carbon nanotubes are multi-walledcarbon nanotubes with a diameter of about 10 nm to about 20 nm.

In block S102, the carbon nanotube film includes a plurality of carbonnanotubes. Adjacent carbon nanotubes are joined end to end by van derWaals attractive force therebetween along a longitudinal direction ofthe carbon nanotubes. The plurality of carbon nanotubes is arrangedalong a direction substantially parallel to an axial direction of thecarbon nanotube. Referring to FIG. 4, each carbon nanotube film includesa number of successively oriented carbon nanotube segments 122 joinedend to end by Van der Waals attractive force therebetween. Each carbonnanotube segment 122 comprises a number of carbon nanotubes 124substantially parallel to each other, and joined by Van der Waalsattractive force therebetween.

In block S103, the number of layers of the carbon nanotube films rangesfrom about 800 layers to about 1500 layers. In one embodiment, thenumber of layers is about 900 layers to about 1200 layers.

In block S12, the electric field at the interface 100 could be changedby a variety of methods.

Method One

The electric field at the interface 100 can be changed by applying anexternal electric field E. Referring to FIG. 2, a directionperpendicular to the interface 100 and from the metallic thermalconductor 10 to the non-metallic thermal conductor 20 is defined as afirst direction; a direction perpendicular to the interface 100 and fromthe non-metallic thermal conductor 20 to the metallic thermal conductor10 is defined as a second direction. The external electric field E isapplied to adjust the electric field at the interface 100 by changingthe direction and/or strength of the external electric field E. In oneembodiment, the interfacial thermal resistance at the interface 100 canbe increased by increasing the magnitude of the external electric fieldE in the first direction.

Method Two

The electric field at the interface 100 can be changed by applying abias voltage U₁₂. Referring to FIG. 5 and FIG. 6, the metallic thermalconductor 10 and the non-metallic thermal conductor 20 are respectivelyconnected to a voltage source. The bias voltage U₁₂ between the metallicthermal conductor 10 and the non-metallic thermal conductor 20 dependson the shape, the size, and the material of the metallic thermalconductor 10 and the non-metallic thermal conductor 20. The bias voltageU₁₂ between the metallic thermal conductor 10 and the non-metallicthermal conductor 20 can be adjusted from about −3V to about 3V. In oneembodiment, the bias voltage U₁₂ ranges from about −1V to about 1V. FIG.6 shows the amplitude ratios of temperatures monitored by infraredthermometer I and II, respectively. It can be seen that all theamplitude ratios of positive bias are larger than that of negative bias.And larger amplitude ratio indicates decreased thermal diffusivity,which means that the thermal diffusivity is large with negative biaswhile the thermal diffusivity is small with positive bias. When0V<U₁₂<0.2V, the interfacial thermal resistance at the interface 100increases as U₁₂ increases; and when −0.9V<U₁₂<−0.4V, the interfacialthermal resistance at the interface 100 decreases as U₁₂ decreases.

In one embodiment, the block S12 can further include: obtaining anelectric field-interfacial thermal resistance relationship by measuringthe interfacial thermal resistance of the interface 100 under differentelectric fields.

FIG. 7 shows an embodiment of a thermal transistor 50 a. The thermaltransistor 50 a includes a metallic thermal conductor 10, a non-metallicthermal conductor 20, and a thermal resistance adjusting unit 30 a.

Both the metallic thermal conductor 10 and the non-metallic thermalconductor 20 are made of heat conductive materials. The metallic thermalconductor 10 can be copper, aluminum, iron, gold, silver, or the like.The non-metallic thermal conductor 20 can be made of electricalconductive material, such as carbon nanotubes, graphene, carbon fibers,or the like.

The shape of the metallic thermal conductor 10 and the non-metallicthermal conductor 20 are not limited. The thickness of the metallicthermal conductor 10 can be ranged from about 0.1 mm to about 1 mm. Thethickness of the non-metallic thermal conductor 20 can be ranged fromabout 30 μm to about 120 μm. The smaller are the thicknesses of themetallic thermal conductor 10 and the non-metallic thermal conductor 20,the easier it is to observe the change of interfacial thermalresistance.

In one embodiment, the metallic thermal conductor 10 is a copper slicewith a dimension of 15 mm×15 mm×0.5 mm, and the non-metallic thermalconductor 20 is buckypaper with a dimension of 15 mm×15 mm×52 μm.

The metallic thermal conductor 10 is closely in contact with thenon-metallic thermal conductor 20, so heat can be transferred as much aspossible between the metallic thermal conductor 10 and the non-metallicthermal conductor 20. The density of the buckypaper ranges from about1.2 g/cm³ to about 1.3 g/cm³.

The metallic thermal conductor 10 includes a first surface 11 and asecond surface 13, and the non-metallic thermal conductor 20 includes athird surface 21 and a fourth surface 23. The first surface 11 and thethird surface 21 are in contact with each other to form an interface100. The second surface 13 and the fourth surface 23 are input/outputends of the thermal transistor 50 a.

In one embodiment, the first surface 11 is opposite to the secondsurface 13, the third surface 21 is opposite to the fourth surface 23,and the surfaces of the first surface 11 and the third surface 21 needto be smooth to ensure good contact.

The thermal resistance adjusting unit 30 a is used to generate andchange an electric field at the thermal interface 100. In oneembodiment, the thermal resistance adjusting unit 30 a includes avoltage source 37 electrically connected to the metallic thermalconductor 10 and the non-metallic thermal conductor 20, respectively.The voltage source 37 controls the potentials of the metallic thermalconductor 10 and the non-metallic thermal conductor 20. The voltagebetween the metallic thermal conductor 10 and the non-metallic thermalconductor 20 is defined as bias voltage U₁₂. The range of the biasvoltage U₁₂ can range from −2V to 2V.

The thermal resistance adjusting unit 30 a can further include a firstcontrol unit 35 a electrically connected to the voltage source 37. Thefirst control unit 35 a is used to control the voltage source 37 tooutput a certain voltage. The first control unit 35 a stores a mappingtable of bias voltage U₁₂-interfacial thermal resistance. According tothe mapping table, the first control module 35 a can obtain a certainbias voltage corresponding to a given interfacial thermal resistance.

The thermal transistor 50 a can further include a shell 40. The metallicthermal conductor 10, the non-metallic thermal conductor 20, and thethermal resistance adjusting unit 30 a are disposed in a sealed spaceformed by the shell 40 which can reduce interference from externalairflow.

FIG. 8 shows an embodiment of a thermal transistor 50 b. The thermaltransistor 50 b includes a metallic thermal conductor 10, a non-metallicthermal conductor 20, and a thermal resistance adjusting unit.

The thermal transistor 50 b in this embodiment shown in FIG. 8 issimilar to the thermal transistor 50 a in FIG. 7, except that thethermal resistance adjusting unit in this embodiment is used to generatean electric field E.

The thermal resistance adjusting unit is a parallel plate capacitor. Theparallel plate capacitor includes a first plate 31 and a second plate 33opposite and parallel to the first plate 31. Both the first plate 31 andthe second plate 33 are electrical conductive plate.

The metallic thermal conductor 10 and the non-metallic thermal conductor20 are disposed between the first plate 31 and the second plate 33.

The thermal resistance adjusting unit further includes a second controlunit 35 b used to control the electric field E generated between thefirst plate 31 and the second plate 33. The second control unit 35 bincludes a voltage source 37 and an angle adjusting unit 353. Thevoltage source 37 is electrically connected to the first plate 31 andthe second plate 33, respectively. The angle adjusting unit 353 isconnected to the first plate 31 and the second plate 33, and used tocontrol the angle (a) between the interface 100 and the two plates 31,33.

The second control unit 35 b can further store a mapping table ofelectric field E-interfacial thermal resistance. According to themapping table, the second control unit 35 b can obtain a certainelectric field E corresponding to a given interfacial thermalresistance.

Referring to FIG. 9, a thermal logical device can be obtained based onthe thermal transistors above. The metallic thermal conductor 10includes a first surface 11 and a second surface 13. The non-metallicthermal conductor 20 includes a third surface 21 and a fourth surface23. The first surface 11 and the third surface 21 are in contact witheach other to form an interface 100. One of the second surface 13 andthe fourth surface 23 serves as input end, and the other surface servesas output end. The second surface 13 and the fourth surface 23 arethermally connected to a heat source or other thermal device. Thethermal connection may be through thermal conduction, thermal radiation,and thermal convection.

Referring to FIG. 10, a method for making a thermal transistor isprovided. The method includes, at least the following blocks:

S21, providing a metallic thermal conductor 10 and a non-metallicthermal conductor 20;

S22, contacting the metallic thermal conductor 10 and the non-metallicthermal conductor 20 to form an interface 100; and S23, contacting themetallic thermal conductor 10 to a first voltage and contacting thenon-metallic thermal conductor 20 to a second voltage.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the forego description, together with details of thestructure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, including inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including, the fullextent established by the broad general meaning of the terms used in theclaims.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. The description and the claims drawn to a method may includesome indication in reference to certain steps. However, the indicationused is only to be viewed for identification purposes and not as asuggestion as to an order for the steps.

What is claimed is:
 1. A thermal transistor, comprising: a metallicthermal conductor, a non-metallic thermal conductor, and a thermalresistance adjusting unit; the metallic thermal conductor and thenon-metallic thermal conductor are in contact with each other to form athermal interface; and the thermal resistance adjusting unit isconfigured to generate a bias voltage U₁₂ between the metallic thermalconductor and the non-metallic thermal conductor.
 2. The thermaltransistor of claim 1, wherein a thickness of the metallic thermalconductor ranges from 0.1 mm to 1 mm.
 3. The thermal transistor of claim1, wherein a material of the metallic thermal conductor is selected fromthe group consisting of copper, aluminum, iron, gold, silver, and alloythereof.
 4. The thermal transistor of claim 1, wherein the non-metallicthermal conductor is made of electrical conductive material.
 5. Thethermal transistor of claim 4, wherein the electrical conductivematerial is selected from the group consisting of carbon nanotubes,graphene, carbon fibers, and combination thereof.
 6. The thermaltransistor of claim 1, wherein the non-metallic thermal conductor is abuckypaper with a density ranging from 1.2 g/cm³ to 1.3 g/cm³.
 7. Thethermal transistor of claim 1, wherein the metallic thermal conductorand the non-metallic thermal conductor are disposed in a sealed space.8. The thermal transistor of claim 1, wherein the metallic thermalconductor and the non-metallic thermal conductor are disposed in avacuum environment.
 9. The thermal transistor of claim 1, wherein thebias voltage U₁₂ ranges from −3V to 3V.
 10. The thermal transistor ofclaim 1, wherein the thermal resistance adjusting unit comprises avoltage source electrically connected to each of the metallic thermalconductor and the non-metallic thermal conductor; the voltage source isconfigured to control electric potentials between the metallic thermalconductor and the non-metallic thermal conductor.
 11. The thermaltransistor of claim 10, wherein the thermal resistance adjusting unitfurther comprises: a first control unit electrically connected to thevoltage source, the first control unit comprises a memory storing amapping table of the bias voltage U₁₂ versus interfacial thermalresistance.
 12. The thermal transistor of claim 1, wherein the metallicthermal conductor comprises a first surface and a second surface; thenon-metallic thermal conductor comprises a third surface and a fourthsurface; the first surface and the third surface are in direct contactwith each other to form the thermal interface.
 13. The thermaltransistor of claim 12, wherein each of the second surface and thefourth surface is thermally connected to a heat source or thermaldevice.
 14. The thermal transistor of claim 13, wherein the secondsurface and the fourth surface are thermally connected by thermalconduction, thermal radiation, or thermal convection.